Synergistic A-site co-doping of (Na1/2Bi1/2)xBa1−xZn1/3Nb2/3O3 perovskites: doping mechanisms, microstructure and impedance studies

Abstract

This study explores the novel synergistic co-doping of (Na_1/2Bi_1/2)²⁺ ions into the A-sites of Ba(Zn_1/3Nb_2/3)O₃ (BZN) perovskites to optimise dielectric properties and reduce sintering temperatures. Polycrystalline (Na_1/2Bi_1/2)_xBa_1−xZn_1/3Nb_2/3O₃ ceramics (x = 0.1–0.4) were synthesised via solid-state reaction, achieving dense microstructures with relative densities exceeding 92 %. The presence of Na_0.13Bi_1.87O_2.87 and ZnNb₂O₆ transient phases facilitated a significant reduction in sintering temperature from 1200 °C (x = 0.1) to as low as 950 °C (x = 0.4). XRD, Rietveld refinement and TEM confirmed the formation of phase-pure cubic perovskites with Pm $\bar{3}$ m symmetry. Dielectric studies revealed enhanced room-temperature relative permittivity (ε′) and optimised dielectric loss (tan δ), attributed to dipole polarisation induced by 6s² lone-pair electrons of Bi³⁺ and improved grain size. Notably, the composition, x = 0.2 exhibited the lowest tan δ (∼0.0096 at 1 MHz) and highest electrical resistance, representing the optimal balance of dielectric performance. Impedance spectroscopy analysis revealed grain-dominated electrical processes and reduced oxygen vacancies, thereby corroborating the correlation between composition, microstructure and electrical properties. This work highlights the functionality of (Na_1/2Bi_1/2)²⁺ co-doping to enhance the dielectric performance of BZN perovskites while achieving optimal density at reduced sintering temperatures, thus rendering them suitable for applications in Low-Temperature Co-Fired ceramic (LTCC) for advanced electronic devices.